Shrinkage compensating cement

ABSTRACT

A shrinkage compensating cement which includes a composition of Portland cement and a reactive compound which expand upon contact with water. The reactive compound is coated with an alkali soluble, water insoluble material in order to delay the time within which the reactive compound will expand. Quicklime or Plaster of Paris are examples of reactive compounds which may be used.

, O 3 Ex awe. $1 aft? a P -14-72 XR 3 649,317 E 1 1 m i 1 J o UnitedStates Patent 1151 3,649,317 Houseknecht 1 Mar. 14, 1972 [54] SHRINKAGECOMPENSATING 3,197,323 7/1965 Rehmar ..106/314 CEMENT 3,027,266 3/1962Wikne ....l06/86 3,021,291 2/ 1962 Thiessen.... ..106/90 [721 T'mdm2,521,073 9/1950 Ludwig ,.106/94 [73] Assignee: Fuller Company 2,465,2783/1949 Schenker et al. ..106/3 I4 [22] Filed: Nov. 12, 1970 PrimaryEmminer jmna E. P0" [21] Appl. No.: 89,040 Assistant Examiner-W. T.Scott Attamey.lack L. Prather and Frank H. Thomson [52] US. CL ..106/90,106/94, 106/97,

106/112, 106/308 0, 106/288 B, 106/314 [571 ABSTRACT [5 1 1 Cl- ..CMII Ashrinkage comesnsating cement includes a composi- [58] Field of Search..106/86, 314, 90, 94, 97, 112, on f pol-and cement and a reactivacompound which 106,308 288 B pand upon contact with water. The reactivecompound is R f CM coated with an alkali soluble, water insolublematerial in order 8 I to delay the time within which the reactivecompound will ex- UNITED STATES PATENTS pand. Quicklime or Plaster ofParis are examples of reactive co un which may be used. 3,303,037 2/1967Klein ..106/314 3,251,701 5/1966 Klein ..106/314 10Clalms, No DrawingsBACKGROUND OF THE INVENTION This invention relates to shrinkagecompensating cement and in particular to a shrinkage compensatinghydraulic cement.

Conventional concrete made with Portland cement usually shrinks duringthe curing process. The shrinkage is usually attributed to the chemicalcombination of the mix water and cement grains which cause a reductionin the volume of the concrete. Virtually all concrete made from Portlandcement will contract to some degree. This shrinkage can result insurface cracking, and if the tensile strength of the concrete isexceeded, the cracking may be deep into the concrete.

In order to overcome the cracking which can result from the shrinkage ofthe concrete, shrinkage compensating or expansive cements have beendeveloped. Such expansive cements are used in various applications. Onesuch application is slabs of concrete. The expansion of the cementcauses pressure to be applied on the forms for the slab after theconcrete has begun to cure and a compressive force is maintained on theconcrete even after the forms are removed. Because concrete hasrelatively high compressive strength, as long as the concrete is held incompression, the likelihood that cracks will develop is substantiallyreduced.

Expansive cements have also been used in prestressed concreteapplications. The expansive cement is used to bring aboutself-stressingof steel reinforcing members contained within the concrete. Expansivecements are particularly useful for three-dimensional prestressing.

Expansive or shrinkage compensating cements are known and one suchcement is set forth in US. Pat. No. 3,155,526. The expansive cementdescribed in this patent is a composition including normal Portlandcement clinker mixed with a special clinker containing a high percentageof alumina. The special clinker may be mixed in amounts from to percentwith the Portland cement for producing varying degrees of expansion.This expansive cement has the disadvantage that a foreign substance isadded to the concrete.

Other expansive cements have been developed, but these also have thedisadvantage that a foreign substance is added to the concrete. Theseprior expansive cements requiring special ingredients can be expensiveto manufacture. The special ingredients require close control andproportioning. Even with such close control, the expansion is oftenerratic and unpredictable.

As referred to herein, the term shrinkage compensating cement" shallinclude cements in which there is a reduction in the amount of shrinkagewhich a conventional cement undergoes during curing, cements whichneither expend nor shrink during curing and cement which expands duringcuring.

SUMMARY It is the principal object of this invention to provide ashrinkage compensating cement which is inexpensive to manufacture andovercomes the disadvantages of prior shrinkage compensating cements.

lt is another object of this invention to provide a shrinkagecompensating cement which does not add any foreign substances to thecured cement.

It is a further object of this invention to provide a novel shrinkagecompensating cement, the composition of which can be controlled to makea concrete which either expands or does not shrink or expand.

In general, the foregoing and other objects of this invention will becarried out by providing a composition comprising Portland cement and areactive compound which will expand upon contact with water; saidreactive compound being coated with an alkali soluble, water insolublematerial. The objects of this invention will also be carried out byproviding the method of producing a shrinkage compensating cementitiousmaterial comprising the steps of coating a reactive compound which willexpand upon contact with water with an alkali soluble, water insolublematerial, and blending the coated reactive compound with Portlandcement.

DESCRIPTION OF THE PREFERRED EMBODIMENT Portland cement nonnally shrinksas it is cured. and it would be desirable to overcome this shrinkingcharacteristic. By the present invention it has been found that suchshrinkage can be compensated for by the addition of an expansive agentto the Portland cement. Since water is added to the cement and aggregatein the making of concrete, the expansive agent is preferably reactiveupon contact with water. Upon reaction with water, the expansive agentshould not add a foreign substance to the concrete. 7

One such expansive material is quicklime (CaO). When water is added toquicklime, it expands and increases in volume by about 20 percent. Thequicklime plus water forms calcium hydroxide (CaO-H-LO Ca(Ol-l),) whichis a normal hydration product of calcium silicates, which comprise 70percent to percent of commercial Portland cement. Thus, the addition ofthe quicklime to the Portland cement will not result in the addition ofany foreign substances to the finished concrete. The addition of thequicklime may be beneficial to the composition as the calcium hydroxidewill react with certain forms of silica to fonn cementitious calciumsilicate. This may add durability to the finished concrete.

A second material which may be used as an expansive agent is Plaster 9fEaris {CaSOfl/ 0). When mixed with water, Plaster of Paris will expandand produce gypsum (CaSOfl H Q-i-lJj l hO-jCaSO ZHZO). Since gypsum isoften added to Portland cement, the addition of Plaster of Paris toPortland cement will not add any foreign substances to the finishedconcrete. However, the Plaster of Paris will expand only about one-halfthe amount that the same volume of quicklime will expand. This factormust be considered in determining the amount of expansive agent to beadded to the Portland cement. Bot lime and Plaster of Parts areinexpensive when cm! additives.

In order for an expansive cement to be useful, it should not expand assoon as water and aggregate are added. However, most of the expansionshould occur within 24 to 48 hours after the concrete has been mixed.After such initial 24 to 48-hour period, the concrete should bedimensionally stable and substantially no further expansion orsubsequent shrinkage should occur. Because the expansive agents which Ihave chosen expand upon contact with water, it is necessary to delaycontact between the expansive agent and water in order to insure thatthe greater part of the expansion takes place within the initial 24 to48-hour curing period. By the present invention, the expansive materialis coated with a water insoluble material. Such coating will prevent thewater from contacting the ex pansive agent until such coating has beendissolved and thereby delay the expansion of the cement.

Since alkalis are naturally formed when water is added to Portlandcement, it has been found to be desirable to make the coating alkalisoluble. When water is added to the cement. the alkalis fonned willdissolve the coating. As the coating is dissolved, the water in thecement will contact the expansive agent thereby expanding the cement.

A coating material which was found to be useful is a wood resincommercially available under the trademark Vinsol." This material meetsthe qualifications of being alkali soluble and water insoluble and hasthe further advantage of being able to be placed in solution withorganic liquids. The ability to be placed in solution with an organicliquid permits easy application of the coating to the expansivematerial.

It has been found that the coating may be applied by placing it insolution with an organic liquid, such as denatured alcohol, and thereactive compound being stirred in the solution. The coated reactivecompound is then dried. Other techniques for applying the coating to thereactive compound may include spraying the coating solution onto thereactive compound. in laboratory applications, the immersion of thereactive compound in the solution of coating material and organic liquidfollowed by filtration and drying proved to be the most successfultechnique for applying the coating material to the reac tive compound.The amount of coating applied to the reactive compound may be varied byincreasing or decreasing the amount of coating placed in solution withthe organic liquid.

Experimentation with the invention was carried out by stirring theexpansive compound in a solution of denatured alcohol and Vinsol forfive minutes followed by suction filtration and drying at 105 C. Thecoated reactive compound was blended with Portland cement in amounts upto 20 percent by weight of the finished product.

Test specimens were of neat cement paste, i.e., no aggregate was added.Water content of the test specimens was kept as close to 25 percent aspossible. After the specimens were molded, they were moist-air cured forone day, then the mold forms removed and length measurements taken.Subsequent length measurements were made at one-day intervals. Identicalspecimens were made without the expansive agent added for purposes ofcomparison.

Three factors affected the expansion of the cement. Those factors were(1) the amount of reactive agent added to the Portland cement, (2) thethickness of coating, and (3) whether moist-air cured or water-submersedcured.

The amount of the coated reactive compound blended with the Portlandcement can be used to control the amount of expansion of the curedconcrete. it has been found that up to 20 percent by weight of thefinished composition may be coated reactive compound. Using the samecoating thickness, a composition of Portland cement and 10 percent byweight of finished product coated reactive compound expanded about 0.19percent after one day, about 0.20 percent after two days and about 0.23percent after 12 days while a composition of Portland cement and 5percent by weight of finished product coated reactive compound expandedabout 0.07 percent after one day, about 0.08 percent after two days andabout 0.13 percent -after 12 days. Each of these test specimens wascured in a similar manner. N0 reversal of the expansion was noted after20 days when measurements were discontinued. It became apparent that ahigher percentage of expansive agent produced a greater expansion, mostof which took place over a shorter period of time.

The thickness of the coating also affects the amount of expansion of thecement. In experimentation, the coating thickness was varied bydissolving greater or lesser amounts of the resin in alcohol. The rangeof coating in solution ran from 1 percent to 50 percent. In all cases,as the strength of the coating solution decreased, and hence thethickness of the coating decreased, the ultimate linear expansion of thecured cement increased. In addition, the thicker the coating, the slowerthe rate of expansion. This is believed to be attributable to the lengthof time it takes to dissolve the coating before the water contacts thereactive compound.

Using an equal amount of coated reactive compound blended with Portlandcement, a comparison of coating thickness was made. A solution ofpercent Vinsol" and 90 percent denatured alcohol resulted in anexpansion of about 0.13 percent after one day, about 0.15 percent in twodays and about 0.19 percent in 12 days. A solution of 1 percent Vinsol"and 99 percent denatured alcohol resulted in an expansion of about 0.26percent in one day, about 0.27 percent in two days and about 0.32percent in 12 days. Again, no tendency to shrink was observed afterdays.

Through experimentation, it was also found that greater and more rapidexpansion occurs when the cement is water-submersed cured than whenmoist-air cured. This is believed to be attributable to the availabilityof enough water in the watersubmersed curing to react with all theexpansive compound. With a 10 percent by weight reactive compoundcomposition,

water-cured cement expanded about 0.18 percent after one day, about 0.20percent after two days and about 0.23 percent after 12 days while thesame moist-air cured cement expanded about 0.03 percent after one day,about 0.05 percent after two days and about 0. l 5 percent after 12days. With a 7 percent by weight reactive compound composition,water-cured cement expanded about 0.10 percent after one day, about 0.11percent after two days and about 0.17 percent after 12 days while thesame moist-air cured cement expanded about 0.01 percent after one day,about 0.02 percent after two days and about 0.09 percent after 12 days.Not only did the water cured cement expand more than the moist-air curedcement, but also the expansion took place more rapidly.

From the foregoing, it should be apparent that the amount of expansioncan be controlled by controlling the thickness of the coating and thepercentage of reactive compound added to the Portland cement and whetherwater-submersed cured or moist-air cured. These factors can also be usedto control the rate of expansion. The amount to be added and thethickness of coating can be detennined for any particular applicationthrough routine experimentation.

From the foregoing, it should be apparent that the objects of thisinvention have been carried out. A skrinkage compensating cement hasbeen provided which is inexpensive to manufacture. The reactive compoundis readily available at low cost. The coating material is readilyavailable at a low cost and is inexpensively applied. The expandingagent does not result in the addition of foreign substances to thefinished concrete. The amount of expansion or contraction of thefinished concrete can be controlled by controlling the expansive agentadded to the Portland cement.

It is intended that the foregoing be merely that of a preferredembodiment and that the invention be limited solely by that which iswithin the scope of the appended claims.

1 claim:

1. A composition consisting essentially of Portland cement and areactive compound which will expand upon contact with water; saidreactive compound being coated with an alkali soluble, water insolublematerial and being present in an amount sufficient to compensate forshrinkage during the curing of said cement.

2. The composition of claim 1 wherein said coating material is solublein an organic liquid.

3. The composition of claim 1 wherein said reactive compound isquicklirne.

4. The composition of claim 3 wherein the coated reactive compound isblended with said Portland cement in an amount up to about 20 percent byweight of the composition.

5. The composition of claim 1 wherein the coated reactive compound isblended with said Portland cement in an amount up to about 20 percent byweight of the composition.

6. The composition of claim 1 wherein said reactive compound is Plasterof Paris.

7. The composition of claim 6 wherein the coated reactive compound isblended with said Portland cement in an amount up to about 20 percent byweight of the composition.

8. The method of producing a shrinkage compensating cementitiousmaterial comprising the steps of coating a reactive compound which willexpand upon contact with water with an alkali soluble, water insolublematerial, and blending the coated reactive compound with Portlandcement.

9. The method of claim 8 wherein the coated reactive compound is blendedwith the Portland cement in an amount up to about 20 percent by weightof the cementitious material.

10. The method of claim 9 wherein said reactive compound is coated withan alkali soluble, water insoluble solution by making a solution of anorganic liquid and the alkali soluble, water insoluble material,applying said solution to said reactive compound and drying the coatedreactive compound.

2. The composition of claim 1 wherein said coating material is solublein an organic liquid.
 3. The composition of claim 1 wherein saidreactive compound is quicklime.
 4. The composition of claim 3 whereinthe coated reactive compound is blended with said Portland cement in anamount up to about 20 percent by weight of the composition.
 5. Thecomposition of claim 1 wherein the coated reactive compound is blendedwith said Portland cement in an amount up to about 20 percent by weightof the composition.
 6. The composition of claim 1 wherein said reactivecompound is Plaster of Paris.
 7. The composition of claim 6 wherein thecoated reactive compound is blended with said Portland cement in anamount up to about 20 percent by weight of the composition.
 8. Themethod of producing a shrinkage compensating cementitious materialcomprising the steps of coating a reactive compound which will expandupon contact with water with an alkali soluble, water insolublematerial, and blending the coated reactive compound with Portlandcement.
 9. The method of claim 8 wherein the coated reactive compound isblended with the Portland cement in an amount up to about 20 percent byweight of the cementitious material.
 10. The method of claim 9 whereinsaid reactive compound is coated with an alkali soluble, water insolublesolution by making a solution of an organic liquid and the alkalisoluble, water insoluble material, applying said solution to saidreactive compound and drying the coated reactive compound.